1. Field of the Invention
The invention relates generally to semiconductor power devices. More particularly, this invention relates to new configurations and methods for manufacturing improved quasi-resonant converters by combining an insulated gate bipolar transistor (IGBT) with a lateral diode as a monolithic structure and a packaging configuration without a requirement of co-packaging a separate diode die and without a requirement of specialized wafer backside process.
2. Description of the Prior Art
Conventional technologies to configure and manufacture quasi-resonant converters as power devices still have difficulties and limitations. Specifically, conventional resonant converters, according to an industry standard, typically include an insulated gate bipolar transistor (IGBT) 1 and a co-packaged diode 2, as shown in FIG. 1A. Unlike metal oxide semiconductor field effect transistors (MOSFET), IGBT devices do not have an intrinsic body diode. The P-type collector layer 5 at the bottom of the device prevents a would-be body diode from conducting, as shown in FIG. 1B. The manufacturing costs are increased due to this requirement to assemble and connect two separate dies (IGBT and diode) as a co-packaged assembly. In addition the IGBT must be made smaller in order to accommodate the separate diode die within the same package footprint. This increases the resistance and reduces the current handling capability of the device.
One possible application of a conventional quasi-resonant inverter is for rice cookers that use induction heating. In such an application, soft-recovery is not a required feature for the diode. A high performance diode is not needed—the diode only needs to conduct for a short duration before the IGBT turns on.
A reverse conducting IGBT with a vertical diode formed near the backside of the IGBT die has been provided as shown in FIG. 1C. An N-type implant region 6 in the P-type collector layer 5 allows a P-N junction diode to be formed from the IGBT collector to the emitter, starting from the bottom and meeting the P-type body (or emitter) region 7 at the top of the device. This IGBT with the anti-parallel (reverse-conducting) vertical diode as shown in FIG. 1C requires additional backside processing including forming a mask on the backside for a backside implant. These additional backside processing steps cause the production cost to increase, and are more difficult to carry out. In cases with thin wafer processing, additional backside processing steps with the thinned wafer also increase the risk of wafer damage. Also, with the reverse conducting vertical diode configuration, as shown in FIG. 1C, the device may suffer from snapback during device turn-on.
Therefore, a need still exists to provide new IGBT structure and packaging configuration to resolve the difficulties and limitations now encountered by those of ordinary skill in the art of power device design and manufacture.